The invention relates to a television camera for picking-up a scene and for producing a signal for displaying an image therefrom, a portion of which has an increased resolution.
Such a camera is used in viewers or scene scanning devices which render it necessary to define with precision one portion of the image field, whilst tolerating a lower resolution in the surrounding field of vision.
An invention of this type is disclosed in the British Patent Specification No. 893,918 which discloses a closed-circuit television system by means of which it is possible to obtain from a scene an image having an increased resolution near a reticule. The television system includes a television camera and means rendering it possible for the scanning lines to be nearer to each other in the region containing the reticule. This region then has an increased resolution. The camera is constituted by a television tube for which scanning of the recording beam is such that there is an increased line density in the centre of the image. At the output of the camera the video signal corresponds to an image which is distorted. The image is corrected by the display tube which recovers a non-distorted image. The camera and the display tube must consequently be well-matched and be provided with two identical, non-standard scanning means. The display tube is therefore not of a universal type.
On the other hand, such a camera does not have an adequate reliability and geometrical stability, it requires high and stable analog control voltages. Its bulk is too large for many applications.
The technical problem to be solved is therefore to obtain a camera which does not have these disadvantages. It must have an increased resolution in a portion of the image so as to be matched to conventional display systems, must have a more extensive field of view and be of small dimensions for easy handling.